PX156 - G2 - interactions

scattering

e^{-} (1) + e^{+} (2) \to e^{-} (3) + e^{+} (4)

process 1: an $e^{-}$ emits a photon that is absorbed by an $e^{+}$
process 2: an $e^{+}$ emits a photon that is absorbed by a $e^{-}$
$P (p r o c e s s 1) = P (p r o c e s s 2)$
the scattering can be drawn vertically to average the time evolving

annihilation

every diagram is made up of 'fragments' which can be mixed